A number of presently available adenosin analogs possess antitumor activity. Their usefulness has been limited by their rapid metabolism by adenosine deaminase. 2'Deoxycoformycin (2'dCF), a powerful inhibitor of adenosine deaminase has been able to potentiate the antitumor activity of some adenosine analogs in vitro and in vivo. The purpose of this work was (1) extend those observations to other adenosine analogs and (2) to study the pharmacokinetics of 2' deoxycoformycin and its in vivo effects on adenosine deaminase. BIBLIOGRAPHIC REFERENCES: Adamson, R.H., Zaharevitz, D.W., and Johns, D.G.: Enhancement of the biological activity of adenosine analogs by the adenosine deaminase inhibitor 2' deoxycoformycin. Pharmacology 15: 84-89, 1977. Johns, D.G. and Adamson, R.H.: Enhancement of the biological activity of cordycepin (3'-deoxyadenosine) by the adenosine deaminase inhibitor 2'-deoxycoformycin. Biochemical Pharmacology 25: 1441-1444, 1976.